Aggression and victimization are both risk factors for social-psychological adjustment problems and future psychopathology. The study of the developmental course of aggression and victimization among children is crucial for identifying children most at risk for future psychopathology (Cummings, Iannotti, &Zahn-Waxler, 1989;Keenan &Shaw, 1994). In children, subtypes of aggression and victimization (i.e., physical and relational) have been extensively studied and developmental psychopathologists have documented links between these behaviors and both externalizing and internalizing problems (Dodge, Coie &Lynam, 2006;Crick, Ostrov, &Kawabata, 2007). Peer relations researchers have revealed robust associations between relational aggression and victimization and hostile attribution biases, loneliness, and depressive symptoms (Crick et al., 2007). However, to date, these associations have been concurrent and possible developmental mechanisms have not been studied in prospective designs. Therefore, the proposed study will conduct a secondary data analysis of the NICHD Study of Early Child Care and Youth Development to test three hypotheses. We hypothesize that hostile attribution biases for relational provocations, loneliness and depressed affect with independently partially mediate the prospective associations between relational aggression and relational victimization. PUBLIC HEALTH RELEVANCE: The goal of this research is to better understand the types of behaviors that may be associated with maladaptive developmental trajectories for both boys and girls. The proposed research will permit the field to move closer toward understanding the developmental mechanisms that promote peer victimization and will provide implications for the development of prevention and intervention efforts during middle childhood.